In the subtractive color process, as is well known in the art, a yellow, cyan, or magenta dye-forming coupler (also referred to herein more briefly as yellow, cyan, and magenta couplers) undergoes oxidative coupling in a silver halide emulsion with an oxidation product of an aromatic primary amine color developing agent which is formed by reduction of exposed silver halide grains with the color developing agent to form a color image.
In such a system, a compound having an active methylene group is generally used as a yellow coupler for forming a yellow dye; a compound of a pyrazolone type, a pyrazolobenzimidazole type, or a pyrazoloazole type, etc., is used as a magenta coupler for forming a magenta dye; and a compound having a phenolic or naphtholic hydroxy group is used as a cyan coupler for forming a cyan dye.
Each of these couplers is dissolved in a substantially water-insoluble organic solvent having a high boiling point or a mixture thereof together with an auxiliary solvent, if desired, and added to a silver halide emulsion, or it is added to the silver halide emulsion in the form of an alkaline aqueous solution thereof. In general, the former is superior to the latter with respect to fastness to light, humidity and heat, graininess and sharpness of color, etc.
In addition to the fundamental property cf dye formation, various characteristics are required for such a coupler. Namely, it should have a high solubility in an organic solvent having a high boiling point or an alkaline aqueous solution, it should have good dispersibility and stability in a silver halide photographic emulsion, a dye formed therefrom should be fast to light, heat and humidity, should have excellent spectral absorption characteristics and good transparency, an image formed therefrom should have good sharpness, and importantly, it should have a high color forming density, a high dye forming rate, etc.
Moreover, since conventional yellow couplers usually have high pH dependency, it is necessary to control very carefully the pH condition of the color developing solution. However, the optimum value of pH of the color developing solution is ordinarily varied to some extent depending on the color developing agent used, the coupler used, or the combination of couplers used. Therefore, a yellow coupler which has a low pH dependency is desired.
As a skeleton structure of a yellow coupler, a pivaloylacetanilide type, a benzoylacetanilide type, a malondiester type, a malondiamide type, a dibenzoylmethane type, a benzothiazolyl acetamide type, a malonic ester monoamide type, a benzothiazolyl acetate type, a benzoxazolyl acetamide type, a benzoxazolyl acetate type, a benzimidazolyl acetamide type, or a benzimidazolyl acetate type, etc., are known. Of these couplers, benzoylacetanilide type couplers and pivaloylacetanilide type couplers are advantageous.
Specific examples of these yellow couplers are described in U.S. Pat. Nos. 2,875,057, 3,265,506, 3,408,194, 3,551,155, 3,582,322, 3,725,072, 4,356,258 and 3,891,445, West German Patent No. 1,547,868, West German Patent Application (OLS) Nos. 2,219,917, 2,261,361 and 2,414,006, British patent No. 1,425,020, Japanese patent Publication No. 10783/76, Japanese Patent Application (OPI) Nos. 26133/72, 73147/73, 102636/76, 6341/75, 123342/75, 130442/75, 21827/76, 87650/75, 82424/77 and 115219/77, etc. (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
For the purpose of development of .alpha.-benzoylacetanilide type and .alpha.-pivaloylacetanilide type yellow couplers which satisfy the above-described various requirements, several attempts to modify the structure of the sulfonamido group which is introduced into the anilide nucleus have been hitherto made.
For instance, in U.S. Pat. Nos. 3,933,501 and 3,894,875, yellow couplers are described which have an alkylsulfonamido bond, an alkarylsulfonamido bond, an aralkylsulfonamido bond, a phenylsulfonamido bond or an alkoxyphenylsulfonamido bond at the 5-position of .alpha.-pivaloylacetanilide and in which one of the hydrogen atoms of the active position is substituted with a phenoxy group having a carboxy group, a nitro group, a 4-benzyloxyphenylsulfonyl group, a 2-alkoxyphenylsulfamoyl group, an alkylsulfamoyl group, a 4-hydroxyphenylsulfonyl group, an alkylphenylsulfonyl group, a phenylsulfonyl group, an alkylsulfonyl group, or a cyano group at the 4-position thereof. Of these yellow couplers, those having a 4-hydroxyphenylsulfonylphenoxy group at the coupling active position exhibit a relatively high activity. However, they are susceptible to the change in pH of the color developing solution, and thus have a defect in that properties of dye images obtained therefrom widely fluctuate, and they have another problem in that they have a poor solubility in an organic solvent having a high boiling point.
Also, couplers having a 4-benzyloxyphenylsulfonylphenoxy group at the coupling active position are disadvantageous because of their extremely low solubility in an organic solvent having a high boiling point.
In Japanese Patent Application (OPI) No. 142340/80 (corresponding to European patent No. 17,833A1), .alpha.-acylacetanilide yellow couplers having an alkoxyalkylsulfonamido group at a non-coupling position are described. According to the description made therein, these yellow couplers have a low melting point by introducing an ether bond into a hydrophobic alkyl portion of the alkylsulfonamido group, and as the result they have an improved solubility in an organic solvent having a high boiling point. However, as is apparent from the example shown hereinafter, their color forming property is not necessarily sufficient, and dyes formed therefrom are less fast to light. In particular, they have a problem in that their coupling activity decreases as the reduction of a rate of an organic solvent having a high boiling point to a yellow coupler.
In Japanese Patent Application (OPI) No. 21738/83, .alpha.-acylacetanilide yellow couplers are described having an alkylsulfonamido group which is substituted with a specific substituent (for example, an alkylthio group, an alkylsulfonyl group, an acyloxy group, an alkoxycarbonyl group, an amino group, a carbamoyl group, an imido group, a sulfonamido group, etc.). However, these couplers have only a poor solubility in an organic solvent having a high boiling point and dyes formed therefrom are less fast to light. Also, they have, disadvantageously, a low coupling activity.
In Japanese Patent Application (OPI) No. 121126/79 (corresponding to British Patent No. 2,018,445A), .alpha.-acylacetanilide yellow couplers are described having a sulfonamido group which is substituted with a substituent (for example, a cyano group, a halogen atom, an alkyl group, an aryl group, a heterocyclic residue, etc.) at its nitrogen atom. However, they have only a low coupling reactivity and dyes formed therefrom do not have necessarily sufficient fastness to light, heat and humidity.
In Japanese Patent Application (OPI) No. 42046/83, .alpha.-acylacetanilide yellow couplers are described having three substituents, that is, a halogen atom or an alkoxy group at the 2-position thereof; a halogen atom, an alkyl group or an alkoxy group; and an alkylsulfonamido group or an alkylsulfonamido group substituted with a phenyl group. However, these couplers have large defects in that they are difficult to dissolve in an organic solvent having a high boiling point and in that dyes formed therefrom have only a low fastness to light.
Further, in U.S. Pat. No. 4,401,752, .alpha.-pivaloylacetanilide yellow couplers are described having at the coupling position an aryloxy group which is substituted at the ortho position to the oxygen atom of the aryloxy group with a carbonyl group, a sulfonyl group or a phosphinyl group and having at the 5-position of the acetanilide an alkylsulfonamido group. However, these couplers are disadvantageous because of their low solubility in an organic solvent having a high boiling point.
As described above, yellow couplers which fully satisfy all of the above-described requirements have not yet been provided.